This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A158039 #11 Nov 27 2015 00:32:56 %S A158039 5040,464642640,9271613897280,126088436280779280, %T A158039 1500148651789039497840,16877281623734016459152640, %U A158039 186571560637066991905251295920,2070944486059672103635752020488080 %N A158039 Determinant of power series of gamma matrix with determinant 7!. %C A158039 a(n) = Determinant(A + A^2 + A^3 + A^4 + A^5 + ... + A^n) %C A158039 where A is the submatrix A(1..8,1..8) of the matrix with factorial determinant %C A158039 A = [[1,1,1,1,1,1,...], [1,2,1,2,1,2,...], [1,2,3,1,2,3,...], [1,2,3,4,1,2,...], [1,2,3,4,5,1,...], [1,2,3,4,5,6,...], ...]; note: Determinant A(1..n,1..n) = (n-1)!. %D A158039 G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008. %e A158039 a(1) = Determinant(A) = 7! = 5040. %p A158039 seq(Determinant(sum(A^i,i=1..n)),n=1..20); %Y A158039 Cf. A111490, A158040-A158050. %K A158039 nonn %O A158039 0,1 %A A158039 _Giorgio Balzarotti_ & _Paolo P. Lava_, Mar 11 2009